1. Field of the Invention
This invention relates to a power control apparatus for a solar power generation system.
2. Description of Related Art
A known solar power generation system comprises a solar cell array which converts sunlight to electrical energy and a power control apparatus which converts the power generated by the solar cell array to power in a state suited to the load and supplies the power to the load.
Since the power generated by a solar cell array fluctuates significantly depending upon the amount of solar radiation and the temperature as well as the operating-point voltage and current of the solar cells, the power control apparatus performs maximum power point tracking control (hereinafter "MPPT control") for adjusting the load of the solar cell array to extract the maximum power from the solar cell array at all times.
Since power Pmax at the maximum power point of a solar cell is approximately proportional to the amount of solar radiation, however, there is the danger that the power control apparatus will output excessive power when the solar radiation is intense. Known methods of preventing this include a method of providing an upper limit for the output value of the power control apparatus and limiting the output current of the power control apparatus to a predetermined value thereby to protect the components constituting the power control apparatus from excessive current, and a method of sensing the output power of the power control apparatus and controlling the output power in such a manner that it will not exceed a predetermined value.
However, these methods have an important drawback. Specifically, in a power control apparatus which limits the output current to a fixed value, there are occasions where the output voltage of the power control apparatus fluctuates and exceeds the rated voltage in a case where the output voltage is not dependent solely upon the power control apparatus, e.g., when a commercial AC power system has been connected as the load. As a consequence, there are instances where the output power of the power control apparatus surpasses the rated power even if the output current is limited.
When the output power of the power control apparatus becomes too large, more heat is produced within the apparatus, making it necessary to thermally protect the components constituting the power control apparatus.